There is a wide range of currencies, and currencies consistently exchange pairs. A pair is one currency exchanged relative to another. At the point when one currency in a pair is bought, the other is sold. If a currency is sold, the other in the pair is purchased. Consider heading off to the bank to exchange US dollars for euros since you are going out traveling. The currency pair, for this situation, is the EUR/USD. US dollars are being sold and euros are being purchased.